This project involves the application of the SSES methodological approach to the study of basic cognitive and neuropsychological processes and their modulation by the environment. The primary focus of this research is the continuation and expansion of a longstanding collaboration with Dr. Jordan Grafman (Chief Cognitive Neuroscience Section NINDS) centering on the longitudinal Vietnam Head Injury Study (VHIS). Besides this work with Dr. Grafman, we are also completing analyses and reports of data from SSES cognitive psychological experiments on both normal and abnormal populations, carried out before we stopped conducting such experiments. This year, in our collaboration with Dr. Grafman, we used Structural Equation Modeling techniques to categorize the head injured Vietnam veterans into statistically coherent groups based on the patterns of their brain injuries. This year, we also used structural equation modeling to investigate the factorial structure of cognitive ability in the head injured veterans and matched normal controls. We also collaborated with Dr. Grafman's group in the development of a survey with which his group is currently investigating the interactions between the nature of the veterans' head injuries and how social structurally determined environmental conditions affect psychological and psychosocial functioning. Other analyses, carried out this year on data previously collected by the section from normal and schizophrenic individuals, focus on the implications of different definitions of task-relevance from different theoretical models of how the pre-frontal cortex deals with potentially interfering stimuli in maintaining selective attention.